Ink-jet printing process using polymeric biguanides

ABSTRACT

An ink-jet printing process comprising the steps (a) and (b) in any order or simultaneously: (a) applying by means of an ink jet printer an ink to a substrate in a localised manner to form an image on the substrate; and (b) applying to the substrate a composition comprising a binder and a polymeric biguanide which has a repeat unit of Formula (1) or a salt thereof: wherein X and Y are the same or different and represent divalent organic linking groups.

BACKGROUND OF INVENTION

The present invention relates to an ink jet printing method, torecording sheets, to compositions suitable for use in the preparation ofrecording sheets and to a set of liquids suitable for use in an ink jetprinter.

SUMMARY OF INVENTION

Ink jet printing (IJP) is a non-impact printing technique in whichdroplets of ink are ejected through a fine nozzle onto a substratewithout bringing the nozzle into contact with the substrate. The imagesprepared by IJP desirably meet many demanding requirements. For example,they should be sharp and non-feathered and should also exhibit highwater-fastness, light-fastness, humidity-fastness and optical density.Furthermore the recording sheets printed with the images are preferredto dry quickly so that sheets printed shortly afterwards do not smudgethe image. The sheets preferably do not crack significantly, even whenprinted with pigment-based inks, and they should not markedly affect theshade or hue of the ink in such a way that an incorrectly coloured imageresults. The recording sheets ideally are not such that they sticktogether during storage or after printing.

We have found that the many of these demanding requirements can besatisfied by using the processes, compositions and recording sheetsaccording to the present invention as described in more detail below.

European patent application No. 0 291 214 A2 describes an informationdevice in the form of a substrate which carries concealed informationwhich becomes detectable by suitably treating the substrate, e.g. bywashing. The device could use a number of fixing agents used to writethe concealed information, including polyhexamethylene biguanide(“PHMB”).

SUMMARY DETAILED DESCRIPTION OF INVENTION

According to a first aspect of the present invention there is providedan ink jet printing process comprising the steps (a) and (b) in anyorder or simultaneously:

(a) applying by means of an ink jet printer an ink to a substrate in alocalised manner to form an image on the substrate; and

(b) applying to the substrate a composition comprising a binder and apolymeric biguanide which has a repeat unit of the Formula (1) or a saltthereof:

wherein:

X and Y are the same or different and represent divalent organic linkinggroups.

X and Y are preferably each independently optionally interruptedalkylene, more preferably optionally interrupted C₂₋₁₂-alkylene andespecially C₄₋₈-alkylene; arylene, more preferably C₆₋₁₀-arylene,especially phenylene; and aralkylene, more preferably C₇₋₁₁-aralkylene,especially benzylene or xylylene.

When X and Y are interrupted alkylene, they are preferably interruptedby —O—, —S—, —NH—, —C(═O)— or phenylene.

Examples of preferred alkylene groups represented by X and Y include—(CH₂)₆, —(CH₂)₈—, —CH₂CH(−)(CH₂)₄CH₃, 1,4-2,3- and 1,3-butylene,2,5-hexylene, 2,7-heptylene and 3-methyl-1,6-hexylene.

Examples of preferred interrupted alkylene groups represented by X and Yinclude —CH₂C₆H₄CH₂—, —CH₂OC₆H₄OCH₂—, —CH₂OC₆H₁₀OCH₂—, —(CH₂)₃O(CH₂)₃—and —(CH₂)₂S(CH₂₎ ₂—.

It is especially preferred that X and Y are C₄₋₈-alkylene, moreespecially hexylene.

The nature of the terminating groups on the polymeric biguanide is notbelieved to be critical. However, preferred terminating groups includeacyl, more preferably CH₃CO; H; optionally substituted alkyl, morepreferably optionally substituted C₁₋₁₀alkyl; acyloxy, preferably—OC(O)(C₁₋₄alkyl); halo more preferably F or Cl; cyano; optionallysubstituted amino; a group of the formula:

and optionally substituted phenyl. Preferred optional substituents onthe terminating groups include C₁₋₄-alkyl, halo (especially Cl), nitroand C₁₋₄-alkoxy (especially methoxy). The terminating group at each endof the polymer may be the same or different.

The polymeric biguanide is typically in the form of a mixture of polymerchains, many or all of which are of different lengths. Preferably, thenumber of individual biguanide units in a polymer chain:

taken together, is from 3 to about 80.

In view of the foregoing preferences the polymeric biguanide preferablycomprises one or more poly(hexamethylene biguanide) polymer chains inwhich the individual polymer chains, excluding the terminating groups,are of Formula (2) and salts thereof:

wherein:

n is from 2 to 40.

n is preferably from 2 to 30, more preferably from 4 to 15.

When the polymeric biguanide is a mixture of poly(hexamethylenebiguanide) polymer chains of the Formula (2) it is especially preferredthat the average value of n in the mixture is 12.

Preferably, the number average molecular weight of the polymericbiguanide is from 1100 to 3300.

Preferably the polymeric biguanide is in the form of a salt. Preferredsalts are those with organic or inorganic acids, especiallywater-soluble salts, for example the hydrochloride, gluconate or acetatesalt.

The polymeric biguanides may be prepared by the reaction of abisdicyandiamide of the formula:

with a diamine of the formula H₂N—Y—NH₂; or by reaction between adiamine salt of dicyanimide having the formula:

with a diamine of the formula H₂N—Y—NH₂ wherein X and Y are ashereinbefore defined.

These methods of preparation are described in more detail in GB 702,268and GB 1,152,243 and any of the polymeric biguanides described thereinmay be used in the present invention.

The polymeric biguanide is preferably colourless, or substantiallycolourless.

The binder is preferably a polymeric binder, more preferably awater-soluble or water-dissipatable polymeric binder or a hydrophobicbinder. Preferred water-soluble binders include starches, preferablyhydroxy alkyl starches, for example hydroxyethylstarch; celluloses, forexample celluslose, methylcellulose, hydroxyethylcellulose,hydroxypropylcellulose, hydroxyethyl methyl cellulose,carboxymethlycellulose (and salts thereof) and cellulose acetatebutyrate; gelatin; gums, for example guar, xanthan gum and gum arabic;polyvinylalcohol; polyvinylphosphate; polyvinylpyrrolidone;polyvinylpyrrolidine; polyethylene glycol; hydrolysed polyvinylacetate;polyethylene imine; polyacrylamides, for example polyacrylamide andpoly(N,N-dimethyl acrylamide) and polyacrylamido-2-methyl propanesulphonic acid); acrylamide-acrylic acid copolymers; polyvinylpyridine;polyvinylphosphate; vinylpyrrolidone-vinyl acetate copolymers; vinylpyrrolidone-styrene copolymers; polyvinylamine; poly(vinylpyrrolidonedialkylaminoalkyl alkylacrylates), for example polyvinylpyrrolidone-diethylaminomethylmethacrylate; acid-functional acrylicpolymers and copolymers, for example poly(meth)acrylic acid andcopolymers of (meth)acrylic acid and other (meth)acrylate monomers;amine-functional acrylic polymers and copolymers, for examplepolydimethylaminoethylmethacrylate; acid or amine functional urethanepolymers, preferably those containing dimethylolpropanoic acid and/orpendant or terminal polyethylene glycols; ionic polymers, especiallycationic polymers, for example poly (N,N-dimethyl-3,5-dimethylenepiperidinium chloride); polyesters, preferably those which carrywater-solubilising groups, especially sulphonic acid groups, for examplepolyesters obtainable by polymerising a polyol withsodiosulphoisophthalic acid.

The water-soluble binders are preferred over water-dissipatable bindersdue to their fast dry times and lower tendency to block the fine jetsused in ink jet printers. A combination of water-soluble binders andwater-dissipatable binders can also be beneficial in terms of improvedmechanical strength, reduced tendency for sheets to stick together andgood ink absorbency.

Preferred water-dissipatable binders are water dissipatable polymers,more preferably latex polymers, for example cationic, non-ionic andanionic styrene-butadiene latexes; vinyl acetate-acrylic copolymerlatexes; acrylic copolymer latexes which carry quaternary ammoniumgroups, for example containing copolymerised dimethylaminoethyl(meth)acrylate; and dispersions of polyester, polyurethane,(meth)acrylate or vinyl polymers and copolymers thereof. The polymerdispersions are preferably prepared by emulsion polymerisation or bydispersion into water of polymers prepared by suspension, bulk orsolution polymerisation.

The binder may comprise a single binder or a mixture of two or more ofthe hereinbefore defined preferred binders.

Overall particularly good results are found when the binder ismethylcellulose (to give good mechanical properties),polyvinylpyrrolidone, polyvinylalcohol, polyacrylic acid (to give goodink absorbency) or a combination thereof to give the combined benefitsmentioned above.

Preferably the weight ratio of the binder to the polymeric biguanide isfrom 99:1 to 1:99, more preferably from 60:40 to 15:85, especially from50:50 to 20:80 and more especially from 30:70 to 20:80.

The binder may also contain further ingredients if desired, for examplecatalysts (e.g. to accelerate cross-linking of the binder), polymericfillers (e.g. polymethylmethacrylate particles of 10 to 50 μm diameter),anti-kogation additives, cross-linkers, primers, drying-timeaccelerants, adhesion promoters, defoamers, surfactants, cationic oranionic salts (e.g. an inorganic acid or organic acid salt of anoptionally substituted polyethyleneimine), whiteners and/or inorganicminerals (e.g. to entrap ink, such as silicates and aluminates) to namebut a few.

Preferably the composition contains a cross-linker, preferably in anamount which causes from 0.1 to 5%, more preferably 0.15 to 4%,especially 0.2 to 2% crosslinking of the composition. These levels ofcrosslinking are preferred because they can result in enhancedmechanical strength without adversely affecting ink absorbingproperties.

Suitable crosslinkers include salts of divalent and trivalent metals(e.g. calcium and magnesium acetate). These metals also offer theadvantage of improving water-fastness of resultant prints.

Preferably the composition is applied to the substrate as a liquid.Accordingly it is preferred that the composition further comprises aliquid medium. The polymeric biguanide and binder are preferablydispersed or more preferably dissolved in the liquid medium. The liquidmedium is preferably selected from water; an organic solvent; and amixture of water and one or more water-soluble organic solvent(s).

The composition may be applied to the substrate using any convenientmethod, for example by dip coating, reverse roller coating, K-barcoating, spraying or by means of an ink jet printer.

Preferably step (b) of the process is performed before step (a) orsimultaneously with step (a). It is especially preferred that thecomposition is applied to the substrate as a surface coating prior toforming the image by ink jet printing the ink.

When the composition is applied to the substrate prior to the ink it ispreferred that the composition is dried and/or polymerised (e.g.cross-linked) before the ink is applied. Any suitable drying method maybe used, for example hot air drying. Therefore in a preferredembodiement the process comprises step (b), followed by drying and/orpolymersation of the product of step (a), followed by step (a).

The polymeric biguanide is preferably present on the substrate at aconcentration of up to 20 g·m⁻², more preferably up to 5 g·m⁻²,especially from 0.1 to 2 and more especially from 0.5 to 1 g·m⁻².

When the composition of step (b) is applied to the substrate by means ofan ink jet printer, the ink jet printer is preferably the same as thatused to apply the ink to the substrate. In this embodiment the polymericbiguanide is preferably applied to the substrate just prior to, orsimultaneously with, application of the ink. Preferably the ink jetprinter used to apply the ink and polymeric biguanide has a nozzle or aseries of nozzles in the printer which are dedicated to the applicationof the polymeric biguanide. Thus the printer may be of the ‘five pen’type in which yellow, magenta, cyan and black are applied by four pensand the composition is applied by a fifth pen. A suitable ink jetprinter and a method for its control is described in EP 657 849.

It is to be understood that in all ebodiments of the present inventionthe terms “ink”, “colorant”, “polymeric biguanide” and “binder” extendto two or more of these materials as well as one of them.

A preferred composition suitable for application to the substrate bymeans of an ink jet printer comprises:

(a) from 0.1 to 10 parts of a polymeric biguanide;

(b) from 0.1 to 10 parts of a binder;

(c) from 30 to 60 parts of a water-soluble organic solvent; and

(d) from 35 to 80 parts water;

wherein all parts are by weight and the total number of parts(a)+(b)+(c)+(d)=100.

Preferred water-soluble organic solvents are selected from the listbelow in relation to liquid media for inks.

When the composition is applied to the substrate by means of an ink jetprinter the composition preferably has a viscosity of less than 20 cP at25° C.

Preferably the composition is transparent or colourless when dry.

The ink used in step (a) of the process preferably comprises a liquidmedium and a colorant. Preferred liquid media include water, a mixtureof water and an organic solvent and an organic solvent free from water.

When the medium comprises a mixture of water and an organic solvent, theweight ratio of water to organic solvent is preferably from 99:1 to1:99, more preferably from 99:1 to 50:50 and especially from 95:5 to80:20.

It is preferred that the organic solvent present in the mixture of waterand organic solvent is a water-soluble organic solvent or a mixture ofsuch solvents. Preferred water-soluble organic solvents includeC₁₋₆-alkanols, preferably methanol, ethanol, n-propanol, isopropanol,n-butanol, sec-butanol, tert-butanol, n-pentanol, cyclopentanol andcyclohexanol; linear amides, preferably dimethylformamide ordimethylacetamide; ketones and ketone-alcohols, preferably acetone,methyl ether ketone, cyclohexanone and diacetone alcohol; water-solubleethers, preferably tetrahydrofuran and dioxane; diols, preferably diolshaving from 2 to 12 carbon atoms, for example pentane-1,5-diol, ethyleneglycol, propylene glycol, butylene glycol, pentylene glycol, hexyleneglycol and thiodiglycol and oligo- and poly-alkyleneglycols, preferablydiethylene glycol, triethylene glycol, polyethylene glycol andpolypropylene glycol; triols, preferably glycerol and 1,2,6-hexanetriol;mono-C₁₋₄-alkyl ethers of diols, preferably mono-C₁₋₄-alkyl ethers ofdiols having 2 to 12 carbon atoms, especially 2-methoxyethanol,2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)-ethanol,2-[2-(2-methoxyethoxy)ethoxy]ethanol,2-[2-(2-ethoxyethoxy)-ethoxy]-ethanol and ethyleneglycol monoallylether;cyclic amides, preferably 2-pyrrolidone, N-methyl-2-pyrrolidone,N-ethyl-2-pyrrolidone, caprolactam and 1,3-dimethylimidazolidone; cyclicesters, preferably caprolactone; sulphoxides, preferably dimethylsulphoxide and sulpholane. Preferably the liquid medium comprises waterand 2 or more, especially from 2 to 8, water-soluble organic solvents.

Especially preferred water-soluble organic solvents are cyclic amides,especially 2-pyrrolidone, N-methyl-pyrrolidone and N-ethyl-pyrrolidone;diols, especially 1,5-pentane diol, ethyleneglycol, thiodiglycol,diethyleneglycol and triethyleneglycol; and mono-C₁₋₄alkyl andC₁₋₄-alkyl ethers of diols, more preferably mono-C₁₋₄-alkyl ethers ofdiols having 2 to 12 carbon atoms, especially2-methoxy-2-ethoxy-2-ethoxyethanol.

Examples of further suitable ink media comprising a mixture of water andone or more organic solvents are described in U.S. Pat. No. 4,963,189,U.S. Pat. No. 4,703,113, U.S. Pat. No. 4,626,284 and EP 4,251,50A.

When the liquid medium comprises an organic solvent free from water,(i.e. less than 1% water by weight) the solvent preferably has a boilingpoint of from 30° to 20° C., more preferably of from 40° to 150° C.,especially from 50 to 125° C. The organic solvent may bewater-immiscible, water-soluble or a mixture of such solvents. Preferredwater-soluble organic solvents are any of the hereinbefore describedwater-soluble organic solvents and mixtures thereof. Preferredwater-immiscible solvents include, for example, aliphatic hydrocarbons;esters, preferably ethyl acetate; chlorinated hydrocarbons, preferablyCH₂Cl₂; and ethers, preferably diethyl ether; and mixtures thereof.

When the liquid medium comprises a water-immiscible organic solvent,preferably a polar solvent is included because this enhances solubilityof the dye in the liquid medium. Examples of polar solvents includeC₁₋₄-alcohols. In view of the foregoing preferences it is especiallypreferred that where the liquid medium is an organic solvent free fromwater it comprises a ketone (especially methyl ethyl ketone) &/or analcohol (especially a C₁₋₄-alkanol, more especially ethanol orpropanol).

The organic solvent free from water may be a single organic solvent or amixture of two or more organic solvents. It is preferred that when themedium is an organic solvent free from water it is a mixture of 2 to 5different organic solvents. This allows a medium to be selected whichgives good control over the drying characteristics and storage stabilityof the ink.

Ink media comprising an organic solvent free from water are particularlyuseful where fast drying times are required and particularly whenprinting onto hydrophobic and non-absorbent substrates, for exampleplastics, metal and glass.

Any colorant suitable for ink jet printing may be used in the ink.Preferred colorants are pigments which may be organic (including carbonblack) or inorganic, disperse dyes and water-soluble dyes, morepreferably water-soluble azo dyes.

The colorant preferably has one or more groups for imparting orassisting water-solubility/dispersibility. Examples of such groupsinclude —COOH, —SO₃H, —PO₃H₂, morpholinyl and piperazinyl and saltsthereof.

When the colorant is a pigment the ink preferably also contains asuitable dispersant to give a stable dispersion of the pigment in theink. Preferably the particle size of the pigment used in the ink is lessthan 1 μm.

The ink may contain a single colorant or a mixture of two or morecolorants.

The colorant is preferably present in the ink at a concentration of 0.5to 20 parts, more preferably from 1 to 15 parts and especially from 1 to5 parts by weight based upon the weight of the ink.

The ink may also contain additional components conventionally used inink jet printing inks, for example viscosity and surface tensionmodifiers, corrosion inhibitors, additives to prevent paper curl,biocides, kogation reducing additives, dispersants and surfactants whichmay be ionic or non-ionic.

In a first preferred embodiment of the present invention the coloranthas at least two groups selected from —COOH, —PO₃H₂, morpholinyl andpiperazinyl or salts thereof. More preferably the colorant has at leasttwo groups selected from —COOH and —PO₃H₂ or salts thereof.

It is especially preferred that the colorant is a water-soluble dyewhich has at least two groups selected from —COOH, —PO₃H₂ morpholinyland piperazinyl, or salts thereof. Preferred examples of such dyesinclude the dyes of the Formulae (3) to (8) and salts thereof,especially sodium, lithium and ammonium salts:

wherein:

n is 0 or 1; and

is 2;

 wherein:

X¹ is morpholinyl, piperazinyl or —NHR¹;

R¹ is optionally substituted alkyl (preferably optionally substitutedC₁₋₈alkyl);and each a=2;

 wherein:

each R² independently is alkoxy, —Cl, —OH or amino; and

each t=2;

wherein CuPc is a copper phthalocyanine nucleus.

wherein:

R³ is —OH, —Cl, or C₁₋₄-alkoxy; and

each q is 2.

In the dyes of Formulae (3), (4), (6) and (8) the —COOH is preferablymeta to the azo group (—N═N—).

The compounds of Formula (3) may be prepared using methods analogous tothose described in the art for similar disazo compounds. For example, asdescribed in Examples 1 and 2 of EP 356 080.

The dyes of Formula (4) may be prepared using an analogous process tothat described in Examples 10 and 15 of EP 468 647A.

The dye of Formula (5) may be prepared using a method analogous toExample 1 of EP 468 648, wherein in place of phenylenediamine there isused 2,5-dimethyl-1,4-phenylene diamine.

The dyes of Formula (6) may be prepared using a method analogous to thatdescribed in Example 3 of EP 679 173 B1.

The dyes of Formula (7) may be prepared using a method analogous to thatdescribed in Example 3 of EP 559 309 A2.

The dyes of Formula (8) may be prepared using conventional techniques,for example, using the method described on pages 17 and 18 and Example 1of EP 0 628 088.

Preferred pigments which have at least two groups selected from —COOH,—PO₃H₂ morpholinyl and piperazinyl, or salts thereof include derivativesof pigments from the azo, disazo, condensed azo, thioindigo,indanthrone, isoindanthrone, anthanthrone, anthraquinone,isodibenzanthrone, triphendioxazine, quinacridone and phthalocyanineseries of pigments.

Preferred carbon black pigments in this first preferred embodimentcomprise carbon black particles onto which are attached organic groupswhich carry one or more groups selected from —COOH, —PO₃H₂ morpholinyland piperazinyl, or salts thereof. Examples of such carbon blackpigments are disclosed in U.S. Pat. No. 5,803,959 and U.S. Pat. No.5,630,868.

We have found that when inks which contain a colorant with at least twogroups selected from —COOH, —PO₃H₂, morpholinyl and piperazinyl, orsalts thereof are used in step (a) of the present process, the resultingprints exhibit a reduction in colour-to-colour bleed and a highlight-fastness compared to prints prepared without the polymericbiguanide of step (b).

In view of the forgoing preferences a particularly preferred inkcomprises:

(a) from 0.5 to 20 parts of a water-soluble dye containing at least twogroups selected from —COOH, —PO₃H₂, morpholinyl and piperazinyl;

(b) from 50 to 98 parts water; and

(c) from 2 to 50 parts of water-soluble organic solvent(s);

wherein all parts are by weight and the sum of the parts(a)+(b)+(c)=100.

Preferably the ink contains less than 500 ppm, more preferably less than250 ppm, especially less than 100 μm, more especially less than 10 ppmin total of divalent and trivalent metal ions. The content of halideions in the ink is preferably below 500 ppm. ‘ppm’ means parts permillion by weight relative to the total weight of ink.

The ink jet printer preferably applies the ink (and optionally thepolymeric biguanide) to the substrate in the form of droplets which areejected through a small orifice onto the substrate. Preferred ink jetprinters are piezoelectric ink jet printers and thermal ink jetprinters. In thermal ink jet printers, programmed pulses of heat areapplied to the ink in a reservoir by means of a resistor adjacent to theorifice, thereby causing the ink to be ejected from the orifice in theform of small droplets directed towards the substrate during relativemovement between the substrate and the orifice. In piezoelectric ink jetprinters the oscillation of a small crystal causes ejection of the inkfrom the orifice.

The substrate is preferably paper, plastic, a textile, metal or glass,more preferably paper or a plastic film (especially a transparent film,for example an overhead projector slide). It is especially preferredthat the substrate is paper, a textile or a transparent film.

Preferred papers are plain or treated papers which may have an acid,alkaline or neutral character. Examples of commercially availabletreated papers include HP Premium Coated Paper (available from HewlettPackard Inc), HP Photopaper (available from Hewlett Packard Inc), StylusPro 720 dpi Coated Paper, Epson Photo Quality Glossy Film (availablefrom Seiko Epson Corp.), Epson Photo Quality Glossy Paper (availablefrom Seiko Epson Corp.), Canon HR 101 High Resolution Paper (availablefrom Canon), Canon GP 201 Glossy Paper (available from Canon), and CanonHG 101 High Gloss Film (available from Canon).

Preferred plastic films are transparent polymeric films, especiallythose suitable for use as overhead projector slides, for examplepolyesters (especially polyethylene terephthalate), polycarbonates,polyimides, polystyrenes, polyether sulphones, cellulose diacetate andcellulose triacetate films.

Preferred textile materials are natural, synthetic and semi-syntheticmaterials. Examples of preferred natural textile materials include wool,silk, hair and cellulosic materials, particularly cotton, jute, hemp,flax and linen. Examples of preferred synthetic and semi-syntheticmaterials include polyamides, polyesters, polyacrylonitriles andpolyurethanes.

The prints obtained using the process also exhibit low colour bleed,high print quality and, in some cases, higher light-fastness compared toprints prepared without the polymeric biguanide. Furthermore, theapplication of the polymeric biguanide does not markedly affect theshade or hue of the ink and does not result in the discoloration of theprinted substrate.

According to a second aspect of the present invention there is provideda substrate printed with an image by means of the process according tothe first aspect of the invention. The preferred substrates are ashereinbefore defined in relation to the first aspect of the presentinvention.

Preferably the image is colour image comprising at least two colours,more preferably a colour image derived from a digital camera or ascanner. For example the image may be derived from a file in the .jpg..jpeg, .tif, .tiff, .pcx, .psp, .pdf, .acc, .fdf, .art, .bmp, .dcx,.fpx, .gif, .mic, .mix, .png, .xws, .pbm, .pgm, .ppm, .pnm, .tga, .xifor .xbm file format.

According to a third aspect of the present invention there is provided arecording sheet comprising a substrate bearing on at least one surfacethereof a composition comprising a polymeric biguanide and a binder.Preferably the composition in this third aspect of the invention is in aform of a layer obtained by a process comprising drying and/orpolymerising a composition comprising a liquid medium, a polymericbiguanide and a binder (a layer obtained in this way being hereinafterabbreviated as a “Biguanide Layer”). The Biguanide Layer may be the solelayer of a of a single layer coating on the substrate, or morepreferably a layer which forms part of a multi-layer coating on thesubstrate.

The preferred substrates, polymeric biguanides and binders for use inthe third aspect of the invention are as defined in the first aspect ofthe present invention. It is especially preferred that the substrate isplain paper, treated paper or a transparent plastic film.

Preferably the recording sheet is white or transparent.

When the recording sheet bears the composition in the form of amulti-layer layer coating the Biguanide Layer may be at any position ofthe multi-layer coating, for example it may optionally be the inner-mostlayer in direct contact with the substrate, the outer-most layer, alayer between the inner-most and outer-most layers, or Biguanide Layersmay be present at two or more of such positions. When the outer-mostlayer is not a Biguanide Layer the layers which are further away fromthe substrate than the Biguanide Layer should be permeable or porous toallow ink to come into contact with the Biguanide Layer. In all cases itis however preferred that a Biguanide Layer is present as the outer-mostlayer (i.e. the layer furthest away from the substrate) because thisensures good contact with inks during ink jet printing.

Preferably the recording sheet bears a thin (preferably 0.1 to 9.9 μmthickness) outer Biguanide Layer and a thick (preferably 10 to 50 μmthickness) inner layer which does not contain a biguanide. In this wayrapid dry times and good dye fixation may be achieved as well asreducing the likelihood of the layer ‘cracking’ compared to when thecombination of thick and thin layers is not used. The thick inner layermay be prepared from binders exactly as described above for theBiguanide Layer except that the biguanide is omitted.

The recording sheet preferably has a thickness of from 10 to 1000 μm,more preferably from 50 to 500 μm. The substrate preferably has athickness of from 9 to 990 μm, more preferably from 49 to 499 μm. Thecoating, whether single- or multi-layered, preferably has an overallthickness of from 0.1 to 50 μm, more preferably from 5 to 30 μm,especially from 10 to 20 μm.

The composition is preferably applied to the substrate by the methodsdescribed above in relation to the first aspect of the invention.

The recording sheets may be used as ink receptive sheets in a wide rangeof printing processes, especially ink jet printing. They are able toprovide excellent quality images, often of near photographic quality,having good wet-fastness, light-fastness, gloss and low sticking andcracking properties. The resultant prints usually good optical density,even with black pigment inks which often suffer from a drop in opticaldensity, an unsightly grey appearance and poor image quality whenprinted onto conventional recording sheets. The humidity fastness isalso good. Furthermore the sheets benefit from good storage stabilitywith a low tendency to bacterial decay over time. When the polymericbiguanides are used as a top layer for recording sheets without thebinder the sheets often stick together during storage, particularlyunder humid conditions. Furthermore the polymeric biguanides are oftenwater-soluble in their own right and even if they have an affinity forthe dyes contained in inks this often does not help water-fastness muchbecause the polymeric biguanide-dyes combination is itself readilywater-soluble. By using the process of the present invention the binderfirmly adheres the biguanide to the recording sheet and the problem ofsheets sticking together is generally avoided.

According to a fourth aspect of the present invention there is provideda composition comprising a polymeric biguanide, a binder and optionallya liquid medium, wherein the polymeric biguanide is as defined inrelation to the first aspect of the present invention. Preferred bindersand liquid media are as hereinbefore described in relation to the firstaspect of the present invention. It is especially preferred that thecomposition is suitable for use in an ink jet printer. Thus thiscomposition is preferably as described above as being suitable forapplication to the substrate by means of an ink jet printer comprises.More preferably the composition has a viscosity of less than 20 cP, morepreferably less than 10 cP, especially less than 5 cP, at 25° C. Theselow viscosity compositions are particularly well suited for applicationto substrates by means of ink jet printers having demanding criteria forthe liquids they apply.

According to a fifth aspect of the present invention there is provided aset of liquids suitable for use in an ink jet printer comprising:

(a) a first liquid comprising:

(i) 0.01 to 50 parts, more preferably 0.1 to 30 and especially from 0.5to 10 parts of a polymeric biguanide as defined in the first aspect ofthe invention;

(ii) 50 to 99.8, more preferably 60 to 80 parts of a liquid mediumselected from water, one or more water-soluble organic solvents and amixture of water and one or more water-soluble organic solvents; and

(iii) 0.01 to 50, more preferably 0.01 to 40 and especially from 0.5 to30 parts of a binder;

wherein all parts are by weight and the total number of parts(i)+(ii)+(iii)=100; and

(b) a second liquid which is an ink comprising a colorant and a liquidmedium.

The ink in the set of liquids according to the fifth aspect of thepresent invention preferably comprises:

(i) from 0.5 to 20 parts of a colorant (preferably a water-soluble dye)containing at least two groups selected from —COOH, —PO₃H₂, morpholineand piperazine;

(ii) from 50 to 98 parts water; and

(iii) from 2 to 50 parts of water-soluble organic solvent(s);

wherein all parts are by weight and the sum of the parts(i)+(ii)+(iii)=100.

The preferred polymeric biguanide, colorants, water-soluble organicsolvents and binders are as hereinbefore defined in the first aspect ofthe present invention.

The set according to the fifth aspect of the present invention ispreferably housed in an ink jet printer, i.e. the invention alsoprovides an ink jet printer comprising a printing mechanism and a set ofliquids wherein the set of liquids is as defined in the fifth aspect ofthe present invention. The set of liquids may be contained in one ormore than one cartridge present in an ink jet printer. The inventionalso provides an ink jet printer cartridge comprising a plurality ofchambers and a set of liquids, wherein the liquids are contained inindividual chambers of the ink jet printer cartridge and the set ofliquids is as defined in the fifth aspect of the invention. Theinvention also provides an ink jet printer cartridge comprising achamber and a composition, wherein the composition is contained in thechamber of the ink jet printer cartridge and the composition is asdefined in the fourth aspect of the invention.

The invention is further illustrated by the following examples in whichall parts are by weight unless specified otherwise.

EXAMPLE 1 Recording Sheet Bearing a Single Layer

A mixture of polyacrylic acid (7 parts), polyethyleneglycol (Mw˜400, 1part) and polyhexamethylenebiguanide hydrochloride (“PHMB”, 2 parts) wasprepared in aqueous solution (solids content=10% by weight) and coatedonto Melinex™ D706 film (which carries a primer) using a Meyer bar. Thecoated film was dried at 80° C. for 3 minutes to give a recording sheetbearing a thick outermost Biguanide Layer having a coating weight of 10g/m^(2.)

EXAMPLE 1A Comparative

The method of Example 1 was repeated except that the PHMB was omitted.

EXAMPLE 2 Recording Sheet Bearing Multi-layers (Biguanide LayerOuter-most)

To a solution of polyacrylic acid (10% strength, 100 g) was addedNeoCryl™ CX100 polyfunctional aziridine (0.1 g, from Avecia B. V.) andthe resultant solution was applied to Melinex™ 535 polyester film usinga Meyer bar and dried at 80° C. for 3 minutes to give a thick inner-mostlayer having a coat weight of 10 g/m². A thin outer-most Biguanide Layercomprising of a 75:25 mixture by weight of PHMB and methylcellulose(Methocel™ J5MS, from Dow Chemicals) was applied using a Meyer bar anddried at 80° C. for 3 minutes. The coat weight of the outer-mostBiguanide Layer was 1 g/m^(2.)

EXAMPLE 3 Recording Sheet Bearing Multi-layers (Biguanide Layer betweenInner-most and Outer-most Layers)

To the recording sheet prepared in Example 2 there was applied a layercomprising Neocryl™ BT70 (acrylic latex from Avecia B. V) using a Meyerbar. The sheet was dried at 80° C. for 3 minutes to give a coat weightof this outer-most layer of 1 g/m^(2.)

EXAMPLE 3A Comparative with No Binder

The method of Example 2 was repeated except that the methylcellulose wasomitted from the composition applied as the thin outer-most layer. Inother words this outer-most layer was free from binder.

EXAMPLE 4 Ink Jet Printing

The recording sheets described in Examples 1, 1A, 2 and 3 were placed inthe tray of a Hewlett-Packard HP 660C thermal ink jet printer containingthe standard inks sold with the printer.

The inks contained in the printer were applied to the recording sheetsto replicate an electronic copy of a photograph and the print definitionwas evaluated visually. Water resistance of the prints was evaluated byinclining the prints at an angle of 45°, dropping water (3 ml) through apipette onto the images and assessing the water resistance visually. Theresults are shown in Table 1 below:

TABLE 1 Print Water Extent of Example Definition resistance CrackingStickiness 1 good good high very low 1A* good poor high very low 2 goodgood very low very low 3 good good very low very low 3A good goodmoderate high Notes: 1) Example 1A contained no polymeric biguanide. 2)Example 3A contained no binder.

EXAMPLE 5

Inks A, B, C and D and Fixer A were prepared as follows:

Ink A

3% Pro-Jet Fast Yellow 2™

5% 2-pyrrolidone

5% thiodiglycol

2% Surfynol 465

85% water

Adjust to pH 9.5 with ammonia.

Ink B

3% Pro-Jet Fast Magenta 2™

5% 2-pyrrolidone

5% thiodiglycol

2% Surfynol 465

85% water

Adjust to pH 9.5 with ammonia.

Ink C

3% Pro-Jet Fast Cyan 2™

5% 2-pyrrolidone

5% thiodiglycol

2% Surfynol 465

85% water

Adjust to pH 9.5 with ammonia.

Ink D

3% Pro-Jet Fast Black 2™

9% 2-pyrrolidone

9% thiodiglycol

1% cyclohexanol.

78% water

Adjust to pH 9.5 with ammonia.

Pro-Jet products were obtained from Avecia Inc., USA.

Fixer A

2% hydroxyethyl cellulose

5% PHMB

93% water

Adjust to pH 9.5 with ammonia.

Fixer A was put into one chamber and the coloured ink into anotherchamber of a trichamber Hewlett-Packard HP 660C thermal ink jet printer.The Inks and Fixer A were printed onto Champion Datacopy paper withFixer A being applied immediately before the ink. In the controlexperiments Fixer A was omitted.

The water and light fastness of the resultant prints were evaluated asdescribed below and the results are shown in Table 2.

Light-Fastness Assessment

The prints were dried and mounted, half covered, in an Atlas Ci35aweatherometer and irradiated for 100 hours. The prints were removed andthe spectral coordinates of the exposed and covered portions weremeasured using an X-Rite™938 densitometer. These readings were used tocalculate the colour difference (ΔE) following irradiation. A low figurefor ΔE indicates low fading, i.e. high light-fastness.

Water-Fastness Assessment

The paper printed with the inks in the form of parallel bars wasattached to a support at a 45° angle so that the parallel bars were in ahorizontal direction. A pipette was then used to dispense 0.5 ml ofdistilled water (pH 6-7) onto the print at a position slightly above thetop of the parallel bars, taking care to ensure the run down of waterover the print was as close as possible to a right angle to the printedbars.

The run-down track formed by the water was assessed visually between thesecond and sixth printed bars against a scale of 1-10 where level 10shows no run-down of dye and 1 shows severe run-down of dye. Thus aprint with a high run-down value indicates a high water-fastness.

The run down test was performed 1 minute after printing.

TABLE 2 Ink Fixer A Water-Fastness Light-Fastness (ΔE) Ink A No 8 26 InkB No 6 52 Ink C No 7 15 Ink D No 8 20 Ink A Yes 10 23 Ink B Yes 10 44Ink C Yes 10 11 Ink D Yes 10 16

From Table 2 it can be seen that prints using Fixer A had a higher lightand wet fastness than prints made without using Fixer A.

What is claimed is:
 1. An ink jet printing process comprising the steps(a) and (b) in any order or simultaneously: (a) applying by means of anink jet printer an ink to a substrate in a localised manner to form animage on the substrate; and (b) applying to the substrate a compositioncomprising a binder and a polymeric biguanide which has a repeat unit ofthe Formula (1) or a salt thereof:

 wherein: X and Y are the same or different and represent divalentorganic linking groups.
 2. A process according to claim 1 wherein X andY are each independently optionally interrupted alkylene.
 3. A processaccording to either claim 1 or claim 2 wherein the polymeric biguanidecomprises one or more poly(hexamethylene biguanide) polymer chains inwhich the individual polymer chains, excluding the terminating groups,are of Formula (2) and salts thereof:

wherein: n is from 2 to
 40. 4. A process according to claim 3 whereinthe polymeric biguanide is a mixture of poly(hexamethylene biguanide)polymer chains in which the average value of n in the mixture is
 12. 5.A set of liquids suitable for use in an ink jet printer comprising: (a)a first liquid comprising: (i) 0.01 to 50 parts of a polymericbiguanide; (ii) 50 to 99.8 of a liquid medium selected from water, oneor more water-soluble organic solvents and a mixture of water and one ormore water-soluble organic solvents; and (iii) 0.01 to 50 parts of abinder; wherein the parts are by weight and the total number of parts(i)+(ii)+(iii)=100; and (b) an ink comprising a colorant and a liquidmedium.
 6. An ink jet printer comprising a printing mechanism and a setof liquids wherein the set of liquids is as defined in claim
 5. 7. Anink jet printer cartridge comprising a plurality of chambers and a setof liquids, wherein the liquids are contained in individual chambers ofthe ink jet printer cartridge and the set of liquids is as defined inclaim
 5. 8. A process according to either claim 1 or claim 2 wherein thepolymeric biguanide is in the form of a water-soluble salt.
 9. A processaccording to either claim 1 or claim 2 wherein the binder is awater-soluble or water-dissipatable polymeric binder.
 10. A processaccording to either claim 1 or claim 2 wherein the composition furthercomprises a liquid medium.
 11. A process according to either claim 1 orclaim 2 wherein the composition is applied to the substrate before orduring ink-jet printing of the ink.
 12. A process according to eitherclaim 1 or claim 2 wherein the composition is applied to the substrateby means of an ink-jet printer.
 13. A process according to claim 12wherein the composition has a viscosity of less than 20 cP at 25° C. 14.A process according to either claim 1 or claim 2 wherein the inkcontains less than 500 ppm in total of divalent and trivalent metalions.
 15. A process according to claim 14 wherein the colorant has oneor more groups selected from —COOH, —PO₃H₂, morpholinyl and piperazinylor salts thereof.
 16. A process according to either claim 1 or claim 2wherein the ink comprises a liquid medium and a colorant with at leasttwo groups selected from —COOH, —PO₃H₂, morpholinyl and piperazinyl orsalts thereof.
 17. A substrate printed with an image by means of theprocess according to either claim 1 or claim
 2. 18. A recording sheetcomprising a substrate bearing on at least one surface thereof acomposition comprising a polymeric biguanide and a binder, wherein thepolymeric biguanide has a repeat unit of the Formula (1) or a saltthereof:

wherein: X and Y are the same or different and represent divalentorganic linking groups.
 19. A recording sheet according to claim 18wherein the composition is in the form of a layer obtained by dryingand/or polymerizing a composition comprising a liquid medium, apolymeric biguanide and a binder.
 20. A recording sheet according toclaim 19 wherein the layer is the sole layer of a single layer coatingon the substrate, or a layer which forms pat of a multi-layer coating onthe substrate.
 21. A recording sheet according to either claim 19 orclaim 20 wherein said layer is present as the outermost layer of amulti-layer coating on the substrate.
 22. A composition comprising apolymeric biguanide, a binder and a liquid medium comprising water andwater soluble organic solvent, wherein the polymeric biguanide has arepeat unit of the Formula (1) or a salt thereof:

wherein: X and Y are the same or different and represent divalentorganic linking groups.
 23. An ink-jet printer cartridge comprising achamber and a composition, wherein the composition is contained in thechamber of the ink-jet printer cartridge and the composition is asdefined in claim
 22. 24. A recording sheet according to claim 18,wherein in Formula (1), X and Y are each, independently, alkylene, whichmay, optionally, be interrupted.
 25. A composition according to claim22, wherein in Formula (1), X and Y are each, independently, alkylene,which may, optionally, be interrupted.